This invention relates in general to the field of electro-optics and, more particularly, to a method and system for manufacturing a photocathode.
There are numerous methods and systems for detecting radiation. In one type of detector, photocathodes are used in conjunction with microchannel plates (MCPs) to detect low levels of electromagnetic radiation. Photocathodes emit electrons in response to exposure to photons. The electrons may then be accelerated by electrostatic fields toward a microchannel plate. A microchannel plate is typically manufactured from lead glass and has a multitude of channels, each one operable to produce cascades of secondary electrons in response to incident electrons. A receiving device then receives the secondary electrons and sends out a signal responsive to the electrons. Since the number of electrons emitted from the microchannel plate is much larger than the number of incident electrons, the signal produced by the device is stronger than it would have been without the microchannel plate.
One example of the use of a photocathode with a microchannel plate is an image intensifier tube. The image intensifier tube is used in night vision devices to amplify low light levels so that the user can see even in very dark conditions. In the image intensifier tube, a photocathode produces electrons in response to photons from an image. The electrons are then accelerated to the microchannel plate, which produces secondary emission electrons in response. The secondary emission electrons are received at a phosphor screen or, alternatively, a charge coupled device (CCD), thus producing a representation of the original image.
Another example of a device that uses a photocathode with a microchannel plate is a scintillation counter used to detect particles. High-energy particles pass through a scintillating material, thereby generating photons. Depending on the type of material used and the energy of the particles, these photons can be small in number. A photocathode in conjunction with a microchannel plate can be used to amplify the photon signal in similar fashion to an image intensifier tube. The detector can thus be used to detect faint particle signals and to transmit a signal to a device, e.g., a counter, that records the particle""s presence.
A photocathode may undergo various material processing operations to provide anti-reflection properties, filtering properties, electron transportability properties, and other suitable properties associated with the photocathode. Additionally, a variety of material processing operations may require placing the photocathode into a vacuum chamber and performing the material processing operation under vacuum pressures.
Various types of systems may be used to load the photocathode into the vacuum chamber so that the material processing operation may be performed under vacuum pressures. An example vertical loading system may include a housing and a drive shaft disposed within the housing. The drive shaft may have linearly formed teeth for engaging corresponding teeth of a gear such that rotation of the gear causes movement of the drive shaft relative to the housing. A rotary drive mechanism may be coupled to the gear to provide rotation of the gear, and the rotary drive mechanism may be coupled to the housing such that the gear extends through an opening in the housing to provide engagement of the teeth of the gear with the teeth of the drive shaft. A ladder for retaining one or more photocathodes may be coupled to the drive shaft such that movement of the drive shaft causes movement of the ladder to various positions within the vacuum chamber.
In operation, the photocathodes are positioned on the ladder and a door or other opening providing access to the ladder is closed. A vacuum is then applied to the housing until a vacuum pressure within the housing is substantially equal to a vacuum pressure in the vacuum chamber. Once the vacuum pressures are substantially equal, a gate valve to a processing portion of the vacuum chamber may be opened and the ladder may be lowered into the processing portion of the vacuum chamber by activating the rotary drive mechanism.
Prior systems and methods for manufacturing a photocathode suffer several disadvantages. For example, the components of the housing of the vertical loading system are generally welded together to ensure that the completed housing is operable to maintain vacuum pressures. As a result of the welding processes, angular variations between the various components of the housing may cause a misalignment of the gear extending through the opening in the housing with the drive shaft. The gear-to-drive shaft misalignment may cause improper engagement of the corresponding teeth of the gear and drive shaft, thereby resulting in premature wear and/or damage to the teeth. For example, improper engagement of the teeth may cause cracking and/or chipping of the teeth. The debris from the damaged teeth may then fall downwardly and onto the photocathodes, thereby interfering with the material processing operations performed on the photocathodes. Additionally, downwardly directed forces resulting from the weight of the drive shaft may cause a deflection of the gear relative to the drive shaft, thereby resulting in a misalignment of the gear relative to the drive shaft.
Accordingly, a need has arisen for a better technique having greater flexibility and adaptability for manufacturing a photocathode. In accordance with the present invention, a system and method for manufacturing a photocathode is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed systems and methods.
According to one embodiment of the present invention, a system for manufacturing a photocathode includes a housing having a first end and a second end. The first end of the housing is operable to be coupled to a vacuum chamber. The system also includes a drive support disposed within the first housing. The system includes a shaft disposed within the first housing and a ladder coupled to the shaft. The ladder includes at least one rung to retain the photocathode. The system further includes a drive system supported by the drive support within the housing. The drive system is coupled to the shaft and is operable to translate the shaft relative to the housing to position the rung of the ladder at a predetermined location within the vacuum chamber.
According to another embodiment of the present invention, a method for manufacturing a photocathode includes positioning the photocathode on a rung of a ladder. The ladder is coupled to a shaft, and the shaft is disposed within a housing. The housing is coupled to a vacuum chamber. The method also includes activating a drive system coupled to the shaft to translate the shaft relative to the housing to position the rung at a predetermined location within the vacuum chamber. The drive system is supported by a drive support disposed within the housing. The method further includes activating the drive system to translate the shaft relative to the housing to remove the rung from the predetermined location within the vacuum chamber after removal of the photocathode from the rung.
The technical advantages of the present invention include providing a system and method for manufacturing a photocathode that provides greater flexibility and reliability than prior systems. For example, according to one aspect of the present invention, a drive system extends through an opening in a housing to engage a shaft to provide translational movement of the shaft relative to the housing. The drive system is supported within the housing using a drive support such that cooperation of a spur gear of the drive system with the shaft is substantially unaffected by compression loads generated during operation of the present invention. The drive support also provides for angular adjustment of the spur gear relative to the shaft to ensure proper engagement of teeth of the spur gear with teeth formed on the shaft. Additionally, the drive support provides for positional manipulation of the spur gear toward or away from the shaft to ensure proper engagement of the teeth of the spur gear with the teeth formed on the shaft.
Another technical advantage of the present invention includes greater flexibility than prior systems by providing for angular and rotational adjustment of the ladder relative to the vacuum chamber. For example, according to one aspect of the present invention, an angular adjustment system may be used to modify an angular orientation of the ladder relative to the vacuum chamber. Additionally, according to another aspect of the present invention, a rotational adjustment system may be used to modify a rotational orientation of the ladder relative to the vacuum chamber.